Equity Transactions Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		3 Months Ended	1 Months Ended	3 Months Ended	0 Months Ended	1 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Common Stock	Jul. 19, 2013 Common Stock Dividend Paid [Member]	Sep. 30, 2013 Preferred Stock [Member]	Jul. 15, 2013 Preferred Stock [Member] Dividend Paid [Member]	Mar. 31, 2013 Registered public offering [Member] Common Stock	Feb. 28, 2013 Series A-3 Preferred OP Units [Member] Rate	Jun. 30, 2013 Conversion of Common OP Units [Member] Common OP Units [Member]	Jun. 30, 2012 Conversion of Common OP Units [Member] Common OP Units [Member]	Jun. 30, 2013 Conversion of Common OP Units [Member] Common OP Units [Member]	Jun. 30, 2012 Conversion of Common OP Units [Member] Common OP Units [Member]	Jun. 30, 2013 Repurchase of Equity [Member] Common Stock	Nov. 30, 2004 Repurchase of Equity [Member] Common Stock
Class of Stock [Line Items]
Authorized to be repurchased (in shares)																1,000,000
Remaining number of shares authorized to be repurchased (in shares)															400,000
Conversion of Common OP Units to common stock (in shares)											0	2,000	0	2,000
New shares issued (in shares)									5,750,000
Weighted average sale price (in dollars per share)									$ 45.25
Proceeds from issuance of common stock									$ 249.5
Preferred OP units issued										4.0
Equity, Preferred OP unit, conversion price										$ 53.75
Equity, preferred return rate										4.50%
Dividends per common share:	$ 0.63	$ 0.63	$ 1.26	$ 1.26	$ 0.63
Dividends, Common Stock, Cash						24.1
Preferred Stock, Dividends Per Share, Declared							$ 0.4475
Dividends, Preferred Stock, Cash								$ 1.5